1. Field of the Invention
Ferroelectric films such as SrTiO.sub.3, Pb(Sr,Ti)O.sub.3, Sr.sub.x Ba.sub.1-x TiO.sub.3, etc. provide a means for producing tuneable capacitors since the dielectric constant of the ferroelectric films is tuneable by variation of voltage applied to the ferroelectric films. Because of their intrinsically low losses at high frequencies, these materials can be implemented in a variety of microwave components, including delay lines and phase shifters.
One of the principle applications of delay lines and phase shifters is for phased array antennas. The voltage-controlled ferroelectric film modulates the dielectric constant and hence the time delay of either microstrip or coplanar delay lines. Such phase shifters or tuneable delay lines can be used to phase delay microwave and millimeter wave signals either transmitted or received from the individual radiative elements of the antenna array.
Such tuneable ferroelectric films can be used in a large family of tuneable microwave components and devices such as phase shifters, matching networks, oscillators, filters, resonators, loop antennas, superconducting film elements, etc.
2. Description of the Prior Art
Ferroelectric phase shifters are disclosed in "Ceramic Phase Shifters for Electronically Steerable Antenna Systems", Varadan, V. K., et al., Microwave Journal, January 1992, pp. 116-126.
The use of superconductors for microwave frequency transmission is disclosed in "High-Temperature Superconductivity for EW" Ryan, P.A., Journal of Electronic Defense, August 1992, pp. 48-54.
The dielectric properties of thin films of SrTiO.sub.3 used as dielectric layers in superconducting field effect (FET) like devices is disclosed in "Dielectric properties of SrTiO.sub.3 thin films used in high T.sub.c superconducting field-effect devices", Walkenhourst, A., et al. Appl. Phys. Lett. 60(14), 6 Apr. 1992, pp. 1744-1746.
A superconductor phase shifter using SQUIDS is disclosed in "Monolithic HTS Microwave-Phase Shifter and Other Devices", Jackson, C M , et al Journal of Superconductivity, Vol. 5 No. 4, 1992, pp. 419-424.
The use of superconductive feed networks and antenna elements of antenna arrays is disclosed in "A Survey of Possible Passive Antenna Applications of High-Temperature Superconductors", Dinger R. J et al IEEE Transactions on Microwave Theory and Techniques, Vol. 39, No. 9, September, 1991.
A thin superconducting film antenna is disclosed in "Radiation Efficiency Measurements of a Thin-Film Y--Ba--Cu--O Superconducting Half-Loop Antenna at 500 MHZ", Dinger, R. J., et al. Paper Presented at MTT-S, Boston, June, 1991, pp. 1-4.
The dielectric properties of BST material thin films are disclosed in "Microstructure-Induced Schottky Barrier Effects", in Barium Strontium Titanate (BST) Thin Films for 16 and 64 MBIT Dram Cells, Scott, J. F., et al., circa 1992.